1. Field of the Invention
The present invention generally relates to an aminosilane treatment for rendering surfaces water repellent. More specifically, the present invention relates to the treatment of substrates with hydroxyl containing surfaces such as paper, textiles, cellulosics, and certain inorganic substrates such as silica or alumina with hydridoaminosilanes and certain derivatives thereof to impart an unexpected water repellency to the treated surface. The hydridoaminosilane treated surfaces are devoid of degradative reaction side products. No pretreatment of the surfaces to be rendered water-repellent is required and post treatment is not necessary to remove unwanted reaction side products.
2. Prior Art
It has been known for decades that the vapor phase treatment of hydroxy containing surfaces with organosilicon halides renders the surfaces water repellent. A thorough account describing the methods of this technique and the basic principles involved is set forth in "Chemistry and Technology of Silicones", Noll, W., Academic Press, N.Y. (1968) p. 585. The original patents in this area were first obtained by Patnode (U.S. Pat. No. 2,306,222) and Norton (U.S. Pat. No. 2,412,470). This method has been demonstrated to be successful but requires additional processing steps to completely remove the severely degradative hydrogen halide reaction by-product. Post-treatment process steps such as washing with an aqueous alkali reagent as described by Patnode in U.S. Pat. No. 2,306,222 or treatment with ammonia vapor as described by Norton in U.S. Pat. No. 2,412,470 or rinsing with a concentrated bicarbonate solution as described by Robbart in U.S. Pat. No. 2,783,090 are time consuming and uneconomical. These post treatment processing steps were later eliminated by maintaining careful control over the time temperature conditions during organosilicon halide the treatment as described by Robbart in U.S. Pat. No. 2,824,778 or by limiting the treatment of cellulosic materials to those with a narrow range of moisture content as noted by Robbart in U.S. Pat. No. 3,856,558. These methods described by Robbart are employed so that the hydrogen halide liberated by the reaction of the organosilicon halide with the hydroxyl groups of the cellulose is not immediately dissolved in the moisture containing cellulose. Nevertheless, the hydrogen halide by-product is subsequently removed, not by a chemical method, but a mechanic method such as blow-drying, heating, or a combination of both. Regardless of whether the method is chemical or mechanical, the hydrogen halide reaction by product must be removed before degradation of the treated material occurs. These methods render the overall process intrinsically more complicated.
Other methods which describe the formation of polysiloxane coatings on the surface with other silane derivatives without the subsequent liberation of such degradative reaction products are known. The methods include the use of organoacetoxysilanes as described by Barry in U.S. Pat. No. 2,405,988, organoisocyanatosilanes as described by Klein in U.S. Pat. No. 2,532,559, organoaminosilanes as described by Gilkey in Belgium Pat. No. 657,145, tert-alkoxy aminosilanes as described by Pedlow in U.S. Pat. No. 2,566,363, and alkoxysilanes as described by Thayer in U.S. Pat. No. 2,474,740. These polysiloxane coatings impart a water repellency to the surfaces which they are applied.
In each of these patents it is recognized that the preferred silicon compounds are those which contain at least one non-hydrolyzable organic group attached to the silicon. The remaining groups are preferably readily hydrolyzable. The silicon compound attaches itself to the surface via the formation of silicon oxygen surface bonds by the reaction of surface hydroxyl groups with the hydrolyzable group attached to the silicon, thereby releasing the hydrolyzable group. Once the silicon compound is attached to the surface, the non hydrolyzable organic groups are forced directly outwards. These highly oriented organic groups impart the desired water repellent action of the organosiloxane film. Compounds lacking non-hydrolyzable groups such as SiCl.sub.4 or HSiCl.sub.3 are useless as hydrophobizing agents by themselves, but are useful as crosslinking agents in forming a tighter polymeric network derived from organosilicon halides. This is taught by Norton in U.S. Pat. No. 2,412,470.
An exception to this art is put forth by Pedlow in U.S. Pat. No. 2,556,363 prescribing the use of tert-alkoxyaminosilanes for imparting water repellency to a variety of surfaces. It is immediately recognizable that the tert alkoxyaminosilanes preferred do not contain non-hydrolyzable groups attached to silicon; however, the tert-alkoxy groups are much less readily hydrolyzed than the amine group. The corresponding water repellent action these compounds impart is then assumed to be due to the polyalkoxylsiloxane coating formed on the surface derived from the reaction of adsorbed water or surface hydroxyl groups with the readily hydrolyzable Si--N bond of the monomeric silane. The liberated ammonia is removed by aqueous washing and/or drying, a post processing step.
Other methods describe the use of aminosilanes to render surfaces water repellent in the form of polysilazanes as is taught by Cachemaille in British Pat. No. 593,727 or Cheronis in U.S. Pat. No. 2,579,416; nevertheless, this method is not substantially different in principle from the employment of monomeric organosilicon halides. In light of the fact that polysilazanes are oligomeric aminosilanes, and therefore of higher molecular weight, their use is usually restricted to liquid phase applications applied either neat or dissolved in an inert solvent.